From the time that conventional gas ovens in kitchen stoves were first used, it was recognized that the problem of removing grease, charred food and other waste materials that dropped or spattered onto the interior bottom, side or top walls of the oven during cooking presented great difficulty and inconvenience. The interior walls were difficult to reach. Oven cleaners were frequently very harsh on the user's hands. The waste materials were frequently even more malodorous during removal than they were before the cleaning process was undertaken. The oven cleaners themselves often had disagreeable odors, and sometimes even gave off fumes that were actually harmful to the user. Finally, a good deal of physical effort was always required to clean the oven walls.
Because of these problems, some 20 years or so ago ovens having an automatic cleaning capability were developed. Some of these were of the self-cleaning type, which utilize a so-called pyrolytic cleaning process at an elevated temperature of as much as 900.degree. F. to burn off accumulated waste material following each use of the oven. Others were of the continuous cleaning type involving so-called catalytic cleaning at temperatures in the usual range of temperatures employed during cooking in an oven, as for example 325.degree. F. to 550.degree. F. In either of these automatic cleaning methods, food soil and residue are burned off the interior walls of the oven, and the walls are left clean.
Outdoor cooking with barbecue grills has grown steadily in popularity since about the end of World War II. The widespread use of covered charcoal grills has accelerated this growth in popularity, especially in the last 20 to 30 years. The introduction of covered grills heated by gas has further stimulated the public's interest in outdoor cooking.
Cooking on covered barbecue grills, whether charcoal or gas-fired, ordinarily proceeds at about 200.degree. to about 400.degree. F. Perhaps because of these relatively low temperatures, it appears that prior to applicant's invention no one had considered it possible to utilize either self-cleaning or continuous cleaning for barbecue grills, whether charcoal or gas. To anyone who attempted to design an automatic cleaning barbecue grill, it might very well have seemed impossible to maintain a sufficiently high temperature, and a sufficiently uniform distribution of heat, that such a cleaning cycle could be successfully achieved.
There have been a number of reasons for this. The single walled cavity used in outdoor barbecue grills has not provided much heat insulation. An outdoor grill is frequently unavoidably exposed to a considerable amount of wind. The grill is very often not well enough sealed to retain sufficient heat to sustain a cleaning cycle. Probably most important of all, no one has seemed aware of the importance of extremely careful control of the pattern of heat production, coupled with extremely careful control of a substantially uniform pattern of distribution of heat throughout the grill.
Specifically, it has not been understood prior to the present invention how to position either the gas burner, or the grate that in conventional gas barbecue grills supports pieces of refractory material above the burner, to achieve the high oxidizing temperatures and the substantially uniform distribution of temperatures throughout the interior surfaces of the grill that are necessary in an automatic cleaning grill. Similarly, the importance of careful control of the size of the exhaust outlet or outlets for an automatic cleaning grill has evidently not been understood.
By his novel construction of the gas grill of this invention, applicant has overcome all the problems that have been mentioned, and has successfully produced an outdoor barbecue grill with an automatic cleaning capability.